I'm using Barcode4j and FOP to generate a PDF that contains a barcode. It works perfect on Jboss 5 GA version but on Jboss 7.1 i get following error :

ERROR: 'The first argument to the non-static Java function 'org.krysalis.barcode4j.xalan.BarcodeExt.generate(result-tree, result-tree)' is not a valid object reference.' FATAL ERROR: 'Could not compile stylesheet'

These are the sections of the stylesheet:

xmlns:xsl="http://www.w3.org/1999/XSL/Transform"
xmlns:fo="http://www.w3.org/1999/XSL/Format"
xmlns:barcode="org.krysalis.barcode4j.xalan.BarcodeExt"
extension-element-prefixes="barcode"
exclude-result-prefixes="fo">

barcode generation:

<fo:instream-foreign-object>
<xsl:variable name="barcodeNumber">
  <xsl:value-of select="barcodeNumber" />
</xsl:variable>
<xsl:variable name="barcode-cfg">
  <barcode>
   <intl2of5>
   <height>18mm</height>
   <module-width>0.28mm</module-width>
   <human-readable><placement>none</placement>
   </human-readable>
   </intl2of5>
  </barcode>
</xsl:variable>
<xsl:copy-of select="barcode:generate($barcode-cfg, $barcodeNumber)" />

I'm using jdk 1.6.27,Jboss 7.1

Any help will be appreciated.